This invention relates to improved high dielectric constant ceramic compositions, and remarkably temperature-stable, monolithic capacitors made therefrom. Even more particularly, this invention relates to improved NPO ceramic compositions produced from a BaO, PbO, Nd.sub.2 O.sub.3, Bi.sub.2 O.sub.3 and TiO.sub.2 mixture in which Nd.sub.2 O.sub.3 has been at least partially replaced by the rare earth oxide Pr.sub.6 O.sub.11 or Sm.sub.2 O.sub.3 selectively to shift the composition negatively or positively, respectively.
Most known NPO dielectric compositions (i.e., maximum allowable change in capacitance over temperature range of -55.degree. C. to +125.degree. C. is .+-.30 p.p.m./.degree.C.) have relatively low dielectric constants (K), e.g. in the range of 36 to 60. Although U.S. Pat. No. 3,775,142 discloses NPO compositions containing neodymium oxide (Nd.sub.2 O.sub.3), and having K values as high as 87, such compositions are limited by the fact that they can contain other rare earth oxides in quantities up to only about 1.0 mole percent, and preferably less than about 0.6 percent.
U.S. Pat. No. 3,811,937 also suggests the use of neodymium oxide in the preparation of high temperature ceramic dielectric compositions produced from the ternary system of BaO, TiO.sub.2 and Nd.sub.2 O.sub.3. However, this patent merely suggests that TC values ranging all the way from -1,000 p.p.m./.degree.C. to +200 p.p.m./.degree.C. and K values from 125 to 30, respectively, could be achieved, provided such compositions were to be mixed and sintered with a low firing glass frit. Although it also suggests that calcium titanate can be added to the dielectric composition to produce high negative TC bodies having lower dielectric constants, it does not teach how to produce a series of NPO dielectric compositions based on BaO,TiO.sub.2,Nd.sub.2 O.sub.3 system, and which have unusually high dielectric constants and low sintering temperature characteristics.
It is an object of this invention, therefore, to provide improved NPO dielectric ceramic compositions having a substantially higher K value than prior such compositions.
It is an object also to provide an improved ceramic composition of the type described in which a portion of its Nd.sub.2 O.sub.3 component is replaced by another rare earth oxide selectively to shift its temperature coefficient of dielectric constant either negatively or positively.
Another object of this invention is to produce from certain such compositions improved high fire, high K, ceramic monolithic capacitors.
A further object is to provide an extremely temperature stable monolithic capacitor produced from a dielectric composition in combination with a glass frit which enables the sintering of the mixture at a temperature substantially lower than prior such mixtures.